The performance of an internal combustion engine can be improved by the use of dual camshafts, one to operate the intake valves of the various cylinders of the engine and the other to operate the exhaust valves. Typically, one camshaft is driven by the crankshaft of the engine, through a sprocket and chain drive or a belt drive, and the other camshaft is driven by the first, through a second sprocket and chain drive or a second belt drive. Alternatively, both of the camshafts can be driven by a single crankshaft powered chain drive or belt drive. A crankshaft can take power from the pistons to drive at least one transmission and at least one camshaft. Engine performance in an engine with dual camshafts can be further improved, in terms of idle quality, fuel economy, reduced emissions or increased torque, by changing the positional relationship of one of the camshafts, usually the camshaft which operates the intake valves of the engine, relative to the other camshaft and relative to the crankshaft, to thereby vary the timing of the engine in terms of the operation of intake valves relative to its exhaust valves or in terms of the operation of its valves relative to the position of the crankshaft.
As is conventional in the art, there can be one or more camshafts per engine. A camshaft can be driven by a belt, or a chain, or one or more gears, or another camshaft. One or more lobes can exist on a camshaft to push on one or more valves. A multiple camshaft engine typically has one camshaft for exhaust valves, one camshaft for intake valves. A “V” type engine usually has two camshafts (one for each bank) or four camshafts (intake and exhaust for each bank).
Variable camshaft timing (VCT) devices are generally known in the art, such as U.S. Pat. Nos. 5,002,023; 5,107,804; 5,172,659; 5,184,578; 5,289,805; 5,361,735; 5,497,738; 5,657,725; 6,247,434; 6,250,265; 6,263,846; 6,311,655; 6,374,787; and 6,477,999. A dual mode phaser that switches between Cam Torque Actuated (CTA) mode of operation and Torsional Assist (TA) mode of operation with a secondary valve is known in U.S. Pat. No. 6,453,859. A Cam Torque Actuated (CTA) phaser that uses one high pressure chamber check valve is known in U.S. Pat. No. 7,137,371. Each of these prior known patents appears to be suitable for its intended purpose.